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Old 12-15-2005, 07:33 AM   #1
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Worse Gas Mileage In cold????

Yeah, so my car only has about 4500 miles on it, its a 2004. I used to get about 280 Miles to a tank. Now it seems that since it has gotten alot colder I am only getting about 250 at the most. Any technical reason for this? I haven't changed my driving, about 50/50 Hwy/City. Just wondering if anyone else has noticed this, doesn't make much sense to me.
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Old 12-15-2005, 07:37 AM   #2
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I've lost about 20-30 miles on a tank. I don't think I can say it's from letting the car warm up either.
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Old 12-15-2005, 07:37 AM   #3
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I've never known of a car that didn't get worse mileage in the cold. The nature of the beast.
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Old 12-15-2005, 07:39 AM   #4
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Quote:
Originally Posted by grapes
I've never known of a car that didn't get worse mileage in the cold. The nature of the beast.
Really?? Why?? I don't get it?? I have had 9 cars and I have never know this to happen. Maybe I wasn't paying attention as much? I don't know, please explain, cuz I don't get it.
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Old 12-15-2005, 07:41 AM   #5
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Quote:
Originally Posted by grapes
I've never known of a car that didn't get worse mileage in the cold. The nature of the beast.
Could be Oxygenated gasoline in the winter.
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Old 12-15-2005, 10:00 AM   #6
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I too usually get about 260-280 per tank, now im getting 250 it seems. Im definetely getting worse mileage in the cold. I keep track of MPG on every tank.
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Old 12-15-2005, 10:04 AM   #7
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Quote:
Originally Posted by Roto8
Really?? Why?? I don't get it?? I have had 9 cars and I have never know this to happen. Maybe I wasn't paying attention as much? I don't know, please explain, cuz I don't get it.
Cold air is denser. Denser air in the engine means the ECU must inject more fuel to maintain the correct mixture.

It doesn't just happen to rotarys, it affects piston engines just the same.
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Old 12-15-2005, 10:07 AM   #8
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You also have more air and road friction when it is colder, taking a little more to get those cold tires rolling. But boy, does the car just love this cold air, makes it feel much stronger.
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Old 12-15-2005, 10:23 AM   #9
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A friends of mines parents are in the gas business...they said winter gas is always worse. I forget why, but they said people always get better mileage in the non winter seasons. I had the same issue with my honda civic. As for cold air being denser and requiring the ECU to inject more gas...I am not sure about this..I thought that because cold air was denser, more air can be compressed into the same amount of space, so the result is better combustion...I didnt think the ECU needed to add more fuel. Shouldnt it just be more air in the same amount of space, but the fuel amount should be the same. This is premise behind cold air intakes and why cars have more spunk on cold winter days.
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Old 12-15-2005, 10:25 AM   #10
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I too have noticed that my MPG has dropped with the temps. I have an 04/AT and usually get around 16mpg in the city (I live in a very hilly area). But over the last month my MPG has dropped to under 14mpg, got 13.1mpg last week with temps in the teens and 20s.

I believe main the cause for this is longer warmup period with higher idle speed when it is very cold (<20) and the car has been sitting for a few hours. This has resulted in me finally cleaning out my garage so I can park in it. So far this week I have been able to get a little better MPG just by not having to warm up the car as long in the morning.
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Old 12-15-2005, 10:56 AM   #11
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you have to consider too that cold weather = crappy roads. the rougher the road, the harder the car needs to work to keep it going.
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Old 12-15-2005, 11:33 AM   #12
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Good lord! I have no idea what's wrong with ya - or right, actually...but 280 miles per tank??? Holy ****. Once...just ONCE my car got 250 miles on a tank...took 12 gallons to fill.
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Old 12-15-2005, 11:39 AM   #13
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It's a known fact that in the winter when the ground gets cold, the gas inside the ground tanks condenses as a result. This means you actually get more gas so to speak when you pump a gallon of cold gas than you do in the summer when it's hot. This is why race teams will chill their gas before putting it in the car because it allows them to put denser fuel loads in.

The gas companies have known about this for ages; they used to just figure "less gas in summer, more gas in winter" and allow the two to equal out. However I have no doubt that today's vulture-suit execs have probably done something to the gas during the winter to thin it out so you the customer don't get this benefit anymore. They are of course NOT going to tell you this; as far as you know you think you're pumping the same gas today that you did during the summer. The fact that you guys are seeing reductions in gas mileage pretty much proves it to me. Why? Because it used to be you got BETTER gas mileage in winter since the gas was more condensed; more miles per gallon because it was denser fuel. Cars seemed to have more power and response too.

All this was true with piston engines; maybe the rotary is different but I would not be surprised if the gas companies have done something to "winter fuel" to compensate for the temperature condensing it.
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Old 12-15-2005, 11:40 AM   #14
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It's because most major cities switch their gas to oxygenated gas. Contains ethonal which doesn't have as much power, but alows more complete combustion. (and therefore less air pollution)
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Old 12-15-2005, 11:45 AM   #15
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Cold air is more dense, that means more oxygen in every induction. Between the Mass Airflow Sensor and the exhaust's oxygen sensors, the ECU does know there is more oxygen and adds fuel accordingly. This does give more power, hence the reason for "cold-air" intakes. Tire pressure typically drops a few pounds and adds to rolling resistance if the lax owner hasn't checked and increased pressure as needed. The denser air also increases aerodynamic drag to some degree.
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Old 12-15-2005, 11:50 AM   #16
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Quote:
Originally Posted by alcimedes
It's because most major cities switch their gas to oxygenated gas. Contains ethonal which doesn't have as much power, but alows more complete combustion. (and therefore less air pollution)
That's the spin; the reality? Denser fuel burns more efficiently, and colder fuel is denser fuel. Denser fuel means you'd be getting more per pumped gallon than you do when the fuel is warm as during summer. They can't charge more on this basis so they dilute the gas in effect by "oxygenating" it. All they are doing is replacing fuel with air bubbles so it pumps as a gallon of gas, but it's not quite the same.

When it comes to the oil industry, always look for the money reason as to why they do something, and ALWAYS assume they are doing it because it's in their favor, not yours.
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Old 12-15-2005, 11:50 AM   #17
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Wow, lots of different opinions on this matter huh? Which one is correct though? hmmmmmmmmm
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Old 12-15-2005, 12:23 PM   #18
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info from chevron...

Quote:
The Real World

During the 1992 oxygenated gasoline season, Chevron received a number of calls from drivers reporting fuel economy decreases of 8% to 10% and a few reporting decreases of 15% to 20%. Using the above example of 23 mpg, this would be a decrease to 20.7 mpg (-10%) to 18.4 mpg (-20%). The California Air Resources Board received similar complaints.

To explain why a few drivers experienced greater decreases in fuel economy than expected for oxygenated gasoline, we must look at the other factors which affect fuel economy. The weather, gasoline composition, the driving cycle, and the mechanical condition of the car are four important factors which might act negatively during the oxygenated gasoline season.

Weather

The oxygenated gasoline season begins October 1 or November 1, depending on the area. This coincides with changes in the weather -- lower temperatures and rain or snow -- which reduce fuel economy.

* Summer or winter, a car's fuel economy is lower while it is warming up, a process that takes 5 to 10 miles or urban driving. Factors which make the effect greater when temperatures are lower include: more time spent at idle to defog/defrost windows of cars parked outside, more time spent using a "fuel rich" warm up mixture, and the additional energy needed to overcome higher viscosities of the cold fluids: engine oil, differential oil, and transmission fluid. The effect is magnified by short trips. The fuel economy of a five mile trip can be 5% to 15% lower in winter.4
* One might assume that the energy saved by not running the car's air conditioner would counter-balance some of the low temperature warm up effects. But the air conditioners of many cars operate when the climate controls are on the "defrost" or "defog" setting to improve defogging performance by reducing the humidity of air blown on the windshield.
* Rain or snow on the roadway decreases fuel economy because it offers more resistance to the forward motion of the tires. Loss of traction (tire spinning) also decreases fuel economy.
* Finally, bad weather often results in more bumper-to-bumper travel during commute times. Stop and go driving exacts a heavy fuel economy penalty.

Gasoline Composition

We have already discussed two related changes in gasoline composition which decrease fuel economy: adding oxygenate and adjusting the octane of oxygenated gasoline. Adjusting gasoline volatility for seasonal ambient temperatures also requires changes in gasoline composition. Summer gasoline is given a lower volatility to avoid vapor lock and minimize evaporative losses. Winter gasoline (both conventional and oxygenated) is given a higher volatility to facilitate starting and warmup. The compositional changes required for the shift from summer gasoline to winter gasoline decrease the gasoline's energy content. Depending on the magnitude of the volatility change, the fuel economy of winter gasoline will be 0.5% to 1.5% lower than of summer gasoline.

Driving Cycle

Terrain, traffic conditions, and driving habits all effect fuel economy. The following list gives examples of changes in these factors which will decrease fuel economy. Some of these changes are more likely to occur during the oxygenated gasoline season.

* Winter driving, on the average, tends to consist of shorter, urban trips, while summer driving is more likely to include some longer highway trips. The fuel economy for urban driving is 25% lower than for highway driving at moderate speeds.5
* Stop and go commuter driving decreases fuel economy.
* Highway driving at speeds greater than 55 mph decreases fuel economy.
* Driving up and down hills decreases fuel economy.
* Greater loads (more passengers or more baggage) decreases fuel economy.
* A driver with more aggressive driving habit (e.g., faster acceleration and more frequent braking) than another driver will obtain a lower fuel economy when both drive the same car. At the extreme, the difference my be as large as 25%.

Car's Mechanical Condition

A car which is not properly maintained is likely to have poorer fuel economy. Factors which reduce fuel economy are:

* Wrong timing (spark retard)
* Fouled spark plugs
* Wrong oil grade (too high viscosity)
* Misaligned wheels
* Underinflated tires

These factors have a cumulative impact on fuel economy. It is difficult to estimate the impact's size because the contribution of each component depends on how far it is out of adjustment. The impact can be large; decreases of 10% to 20% in fuel economy are possible.6

Measuring Fuel Economy

Finally, measurement errors can make fuel economy changes appear larger than they actually are. To determine the size of a change, one needs good fuel economy values for the present time and for some (reference) time in the past.

Most people measure fuel economy by filling a car's gas tank and noting the odometer reading, driving for a period of time, and then refilling the tank and noting the new odometer reading. It's not easy to fill the tank to the same level every time: vapor bubbles can get trapped against the top of the tank and the automatic nozzle shutoff system may not bring the gasoline level to the same point in the filler spout. A filling difference of just 0.2 gallons in a 10 gallon purchase represents an error of 2%. Because of this problem, the accuracy of a fuel economy calculation is increased greatly if it is measured over several tankfuls.
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Old 12-15-2005, 01:43 PM   #19
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Except in MN stations are required to pump gas with ethonal (oxygenated) 100% of the time. There are, however, a few stations which apply for waivers from the EPA and still sell non-oxy gas. You will (in an RX8) always get at least 10% (usually closer to 20%) better gas milage with non-oxy fuels than with oxy gas, even if you train your ECU on oxy. This is regardless of temperature. The summers easily reach 90 to 100 degrees and yet oxy gas will still give you at least a 10%-20% reduction in MPG.

Temp is not the issue. Find a non-oxy station and you'll see your MPG go back to about what they were before.
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Old 12-15-2005, 01:57 PM   #20
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i had used 87 octane gas until i found out my mpg went from 13 to 16mpg by going back to 89 octane. i may track it and see if switching again to 92 will make an even bigger jump. my best mpg has only been 19-20 ...
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Old 12-15-2005, 03:04 PM   #21
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Post Oxygenates.....

Quote - "They can't charge more on this basis so they dilute the gas in effect by "oxygenating" it. "

Your government MAKES the oil companies put that crap in gasoline. They would just rather pump good-old dinosaur juice, without all that ethanol/MTBE crap.

I have worked in a gasoline refinery for 20+ years, it's expensive, corrosive, finicky and ruins mileage. It's your government, so you are just getting what you asked for......

The point about "winter" gas is absolutely true - we can blend our butane and lighter components back into the regular gas in the winter, 5 to 10 percent is not unusual! It is awful for mileage, but it has to be there to start a car at minus 30*C, so your mileage suffers for the rest of your trip, to ensure it will start.

Butane is actually high 'Octane', so the blend computer will maximize it, as much as we can get away with.

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Old 12-15-2005, 04:24 PM   #22
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Quote:
Originally Posted by alcimedes
Except in MN stations are required to pump gas with ethonal (oxygenated) 100% of the time. There are, however, a few stations which apply for waivers from the EPA and still sell non-oxy gas. You will (in an RX8) always get at least 10% (usually closer to 20%) better gas milage with non-oxy fuels than with oxy gas, even if you train your ECU on oxy. This is regardless of temperature. The summers easily reach 90 to 100 degrees and yet oxy gas will still give you at least a 10%-20% reduction in MPG.

Temp is not the issue. Find a non-oxy station and you'll see your MPG go back to about what they were before.
You know, now come to think of it, I did change gas stations as in the past 3 weeks as well, went from using Mobile to Stewarts, because is was about 7 cents cheaper. Could be that Stewarts is an oxy station and Mobile was not at the time I was getting gas there. This is very interesting, I had no idea of some of this sutff. Thanks everyone for the efforts!
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Old 12-15-2005, 05:01 PM   #23
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That's the most likely culprit. Oxy gas is almost always cheaper than non-oxy gas, and sometimes when you see a station where the midgrade gas is cheaper than the lowest grade this is why. People think higher octane gas=better gas, which isn't alwasy the case.

Not sure what the laws are in your state, but in most states where they serve up both oxy and nonoxy gas, they're required by law to post somewhere on the pump that it's oxy.

In our state, where everything is required to be oxy, they no longer post it on the pumps. although the handful of stations that sell nonoxy often post that it's for "recreational use or classic automobile use only", and can only be found outside the major cities.
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Old 12-21-2005, 01:41 AM   #24
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I thought everyone knew that the colder the engine, the worse mileage...

This applies to every car. Until the engine is warmed up, mileage will be lower.

Am I missing something? It's 3am here so I probably am.
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Old 12-21-2005, 10:32 AM   #25
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Quote:
Originally Posted by REL_RX8
I thought everyone knew that the colder the engine, the worse mileage...

This applies to every car. Until the engine is warmed up, mileage will be lower.

Am I missing something? It's 3am here so I probably am.
We're talking about the cold weather. Not, the temperature of the engine.
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Old 12-21-2005, 10:32 AM
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